1. Field of the Invention
The present invention relates to video processing and, more particularly, to a method and apparatus for statistically multiplexing services.
2. Description of the Background Art
In digital television systems, such as cable, satellite, and broadcast television systems, transport multiplexers (TMXs) are employed at distribution facilities to process multiple video streams. A TMX typically performs various functions, such as service multiplexing, grooming, video bit-rate transcoding, splicing, and the like. Notably, service multiplexing is the process of combining multiple video streams (also referred to as services) into a single multiplexed stream. Transcoding is the process of partially decoding a video stream, such as an MPEG-2 (moving pictures experts group) elementary stream, followed by a re-encode for the purpose of reducing the video bitrate.
In a distribution facility, some multiplexed services contain a mix of services. Some services in the multiplex are produced by local encoders (“locally encoded services”). Other services in the multiplex are pre-encoded (pre-compressed). The group of services in a multiplex has a particular group bandwidth. In order to multiplex the locally encoded services with the pre-encoded services, the TMX often must adjust the video bit rate of one or more services so that the multiplex fits in the group bandwidth. In current implementations, local encoders are configured to encode services using constant bit rate (CBR) encoding. The TMX then transcodes one or more of the locally encoded services to satisfy the group bandwidth constraint. Such transcoding, however, results in a loss of video quality, particularly when transcoding from a high bit rate to a significantly lower bit rate. Accordingly, there exists a need in the art for a method and apparatus capable of statistically multiplexing locally encoded and pre-encoded services with minimal transcoding of the locally encoded services.